Feature Of The Week 5/1/11: One major cause of Open Angle Glaucoma is the poor outflow of aqueous humor through the Trabecular Meshwork (TM). Potential treatments include the micro-bypass stents, which are implanted in the TM and shunt fluid directly to the Schlemm’s Canal (SC) to reduce intraocular pressure. Implanting the stent with the appropriate orientation near a major collector channel (CC) might maximize outflow of aqueous humor.

As scleral tissue and the TM are not transparent to visible light, OCT using infrared light may be useful in visualizing and locating collector channels, hence could assist the surgeon to optimize the positioning of the implant.

Commercial SD-OCT systems have been used to image SC externally through the sclera. However, the visualization was not sufficient. Because of sclera tissue thickness, SC and its junctions with CC were not easily identified and located. At the same time, external OCT requires total immobilization of the eye to provide stable images, which makes intra-operative application not feasible. Thus, a desired apparatus must be small, usable intra-operatively, and able to image through the TM to visualize collector channels in SC.

Endoscopic OCT systems could potentially overcome these limitations. They are able to penetrate into deep tissues and collect reflected optical signals from desired depth and consequently improve the contrast and visualization of the physiological structures of interest. Furthermore, as their small size, these systems are capable of intra-operatively providing real-time guidance during surgeries.

We developed a forward-imaging needle probe: Paired Angled Rotating Scanning (PARS) endoscopic probe to acquire high-quality OCT images to improve ophthalmic surgery visualization. The prototype probe consisted of two gradient-index (GRIN) lenses, which were housed in two stainless steel needles respectively. The probe scanned the laser beam across a fan shape area by rotating the two GRIN lenses. We applied the probe to guide an OCT laser beam onto human cadaver eye tissue samples to detect CCs. The acquired OCT images clearly show a CC opening on the wall of SC with the channel going into the sclera, from which quantitative measurements were made. The results from OCT and scanning electron microscopy (SEM) show good agreement with each other. Thus, to the best of our knowledge, for the first time, this work successfully clearly located the collector channels’ openings to the Schlemm’s canal and quantitatively measured their structures by depth-resolved OCT imaging. This probe can potentially be adapted to visualize the anterior chamber during trabecular bypass stent implantation surgeries that would benefit a lot from high-fidelity OCT images.